Sound during take off: Vibration with a resonating tone

[Tenutso]

Hi Everyone,

First time posting but I've been reading for a few months. Thanks to everyone for posting useful and helpful information about these kits.  The forums have make it very easy to get started.  I have been enjoying my Magic Pie III kit with 48v 10ah for a few months and recently someone pointed out that a sound during take off might not actually be normal.  I went ahead and created a video to capture the sound in order to get some input. It could be normal but better be sure. Does anyone recognize the sound during each take off in my video. It's a deep and short vibration with a resonating tone that kind of flows through the bike and the frame.

http://youtu.be/pzkNKuSO8Sw

[Leslie]

Is your ride heavy?  Just a bit of case rattle.


Your Pie sounds freaking beautiful.  Just be sure all the case bolts are done up tight with an evenish tension.  If you are a speed power freak, might want some strong spokes on the bad roads or if carting loads.

[Leslie]

And I think that's normal, something to do with, during certain load bearing torque levels, and RPM situations,  when switching clicks on and off at certain speed under torque, it finds the tune of the motor dimensions and make them sing a rumbly grumbly song, all pies literally sing the same tune, basically turns your motor into a vibrator for a second and goes away, you can even hold it at that spot if you have a very heavy weight on a hill.  Trust me, I hear it  lot.  You can hear it phase in and out quickly. More load it lasts longer. The only solution is to get a very expensive controller that can compensate for these disruptions, back the motor off to Granma mode, or make sure nothing is rattling on your bike.  I have had this on all my GM motors, and I never used anything but GM motors and controllers, Infineon, and one off market controller, all my motors growl a little on the hard starts.

[Morgen 3Eman]

Hi Tenuto,

I agree with Les, it sounds pretty normal.  I use a cast 20" MP3 with an Infineon based controller, and my Pie sounded the same as it did on the GM controller.  I assume it is just the motor structure going through a resonance point. 

TTFN,
Dennis

[Tenutso]

I'm about 210 lb on a full suspension mountain bike with 26" rear wheel motor. It performs well.  I'm averaging a top speed of about 38-40km. Thanks for the input - really helpful. I don't have any other motors or bikes to compare it to as it's still quite a rare thing around here. The only thing I don't enjoy about the bike is the deep knobby tire treads. It's noisy and probably not the most efficient tread in the summer.

[Leslie]

Ha, those noisy tires.  Thats awesome, you worry now about noisy tires.   Nice quite motor otherwise.  I often compare the performance and efficiency with a similar powered internal combustion motor by how much noise they make.  Noisy motors often run hot unless they are an audio speaker.  Motors are not supposed to be designed to be noise generators.

What ever you do, if you see an $80 tire, and it looks a bit sturdier than the $30 tire, chances are the $30 will have you changing it in 4 weeks, while the more expensive tire will last you 6 mths. 

The Knobbies are essential for my roads, the slicks seem to pick up more nails, and sharpies over a ride and they push deeper into the tires, like a piece of glass in your foot, then you get a puncture..  The knobbies give you more hit an miss ratio, thus much more usage over the long term.  If you got good roads, then definitely go with the slick tires.